390 IMMUNOLOGY 



eiioii of their appearance was first observed by Felix and Weil and 

 is regarded as being- sufficiently constant to be of value in the diag- 

 nosis of typhus fever. The agglutination of Proteus X19 by the 

 serum of a typhus fever patient is called the Felix-Weil reaction. 

 Castaneda and Zia (1933) have demonstrated a common antigenic 

 factor in Typhus Rickettsia and Proteus X19. This accounts, ap- 

 parently, for the presence of agglutinins for the latter. 



Tularemia — Specific and Cross Reactions With Br. Abortus 

 Antigens. — In clinical cases of tularemia, it is not uncommon to 

 observe an increase in agglutinins for Br. ahortus. Conversely, in 

 undulant fever, there may be an increase of agglutinins for P. 

 tuhrensis. Francis (1926) has investigated the relative occurrence 

 of agglutinins for Br. ahortus in the blood stream of patients 

 suffering from tulai'omia and has tabulated his results as shown 

 in Table IX. 



Table IX 



U. S. PiTBLic Health Reports, .TrxE, ]02fi 



Permission of author and Surgeon General, U. S. Public Health Service. 



